1. Field of the Invention
The present invention concerns a method for transmitting information at high speed by allocation of multiple bursts. It also concerns an associated receiving method and device.
2. Description of the Prior Art
In a time division multiple access (TDMA) system each user utilizes a given frequency during a given time slot, the other time slots being reserved for other users. The structure of the signal is based on the "burst" concept. A burst contains start and end symbols which are known to the receiver, information symbols which constitute the payload of a burst and a learning sequence known to the receiver and used for synchronization, channel estimation and equalization.
The efficiency of a burst is defined as the ratio: ##EQU1##
The efficiency eu is proportional to the payload. A specific number Nb of these bursts is inserted into a higher entity called a frame which repeats periodically. The data signalling rate for a user with access to one burst per frame is: ##EQU2## where ncu is the number of information symbols transmitted by this user, i.e. the payload of his burst, and dt is the duration of a frame.
In communications by radio the behavior of the transmission channel varies. In order to be able to detect a received burst and determine the value of the information symbols, the receiver must know how the transmission channel behaves during the transmission of the burst. An estimator device uses the learning sequence in the middle of the burst for this purpose. The characteristics of the learning sequence are chosen according to the characteristics of the transmission channel. The further the burst extends on each side of the learning sequence, i.e. the longer the payload relative to the learning sequence, the less reliable at the ends of the burst is the impulse response of the channel as estimated at the center of the burst. The learning sequence is usually located in the middle of the burst and the payload, whose size depends on that of the sequence, is equally distributed on each side of it in order minimize fluctuations of the channel and therefore variations in its impulse response over the duration of the burst.
If a user needs to transmit at a data signalling rate greater than that corresponding to one burst, one solution is to allocate that user a plurality of not necessarily adjacent bursts in the same frame. If he is allocated n bursts, then this user acquires a data signalling rate equal to: ##EQU3##
On the other hand, the transmission efficiency is still equal to eu.
An object of the present invention is to propose a method of transmitting information at high speed by allocation of multiple bursts which also contributes to improving transmission efficiency.